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Author Topic: Quick spark plug question  (Read 784 times)

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Offline oldk6guy

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Quick spark plug question
« on: June 22, 2011, 03:53:28 PM »
this is the spark plug i pulled from the non-running 750k5 that i bought.  Am I wrong or is the "6" in the part number the heat range?  how bad is that?


also wanted to know if i can or if i should or shouldnt run these?

motor is being rebuilt with 65mm pistons, dont know if that matters.
plug on top is a champion( not literally, thats just the brand name ;)).  bottom plug is NGK.

thanx guys.
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76 cb750 k6: 4 into 4 exhaust, open air horns on carbs.

Offline fmctm1sw

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Re: Quick spark plug question
« Reply #1 on: June 22, 2011, 04:05:40 PM »
Looks too rich to me.  If you are going to alter it from stock configuration, you will need to do plug chops to get your jetting right anyway.  If you're rebuilding the engine, I wouldn't worry about it too much right now.  As far as those plugs, the "R" may indicate resistor.  Make sure resistor plugs are right for a K5 (don't know off top of my head)...
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This is a help or GTFO thread.

1973 CB350F
1973 CB350G
1975 CB550K
1983 GL650I
1973 CB750K3 (http://forums.sohc4.net/index.php?topic=92888.0)
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Offline oldk6guy

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Re: Quick spark plug question
« Reply #2 on: June 22, 2011, 04:34:32 PM »
the "R" is for resistor.  i asked the parts guy at the honda dealership about that and he said it didn't matter.  is he wrong?  he didnt seem like the brightest bulb... also,  what is a plug chop?
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76 cb750 k6: 4 into 4 exhaust, open air horns on carbs.

Offline TwoTired

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Re: Quick spark plug question
« Reply #3 on: June 22, 2011, 05:51:17 PM »
 Ok  I'll type this yet again.

You should have some resistance in the spark leads.  Either in the wire, in the plug cap, or in the spark plug.  Note the OR not AND.

If you have the stock coils (didn't tell us) then you should have non resistor wires, a resistor in the spark plug cap, and no resistor in the spark plugs.

The first plug was a champion plug and uses different numbers to indicate heat range than NGK.  They do not cross directly.

With the stock coils, it DOES matter how much total resistance is in the spark circuit.

The CB750 uses NGK D8ES plugs, normally.  If operating in cold weather, D7ES will make operation a bit nicer as it is a hotter plug.

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Lloyd... (SOHC4 #11 Original Mail List)
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Offline oldk6guy

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Re: Quick spark plug question
« Reply #4 on: June 22, 2011, 06:17:57 PM »
sorry for the lack of information.  i would have posted it but i dont know.  the coils do appear to be stock, that's about all i know.  i dont know how to tell if the wires have resistance or not, i dont believe they are stock but i could be wrong.  i am seeing a lot of mentioning of spark plug caps when i search.  i have no idea what that is. im an auto mechanic and i have never in my life heard that term.  nor do i know how to tell if i have them or need them or where they go.
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76 cb750 k6: 4 into 4 exhaust, open air horns on carbs.

Offline keiths

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Re: Quick spark plug question
« Reply #5 on: June 22, 2011, 06:38:57 PM »
If your coils are stock, then your wires and caps are most likely stock also.
The caps are the Bakelite ends of the wires that the plugs plug into. Unscrew them from the wires and check the resistance with a meter. I have read that most Honda motorcycles use 5K resistor caps until the early 90s. If they are more than 10K replace them. I just ordered a set from crc. Three of my caps were 12K and one was 50K. It should make a huge difference.
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